So-called ARAM's (Audio Random Access Memories) are preferred as memory modules for digital voice storage. These are so-called DRAM's (Dynamic Random Access Memories) typically have a maximum number of memory errors up to 0.2%(e.g., a maximum of 0.2% errors in memory), as promised by the manufacturer (Texas Instruments, Inc.; 4 Mega Bit ARAM TMA 44 400). In addition, these memory modules have an area that is guaranteed free of errors.
Methods that were known until now for determining the remaining errors operate in accordance with the following principle. After a system containing the memory module is switched on, the memory module is tested for errors by a testing program. The addresses of faulty areas are determined. These addresses are then stored in a different memory. This other memory is e.g. a so-called SRAM module (Static Random Access Memory). The implementation of this method takes about 30 seconds. When the data are written into the memory module, and before the final entry of the data, a test is performed of whether the area into which it will be written is listed as faulty in the SRAM. If the area is listed as faulty, either the next area is used, or a correction value is recorded in the SRAM.
A similar method is used when data is read out from the memory module. However, this method only detects errors while the system is being switched on. It is not possible to correct errors that were not detected during the switching on.
Another possibility is described in the German Patent Application P 42 04 929.6. It describes a digital voice storage system with a memory control, which is able to detect remaining errors and to delete the detected errors with their corresponding addresses in a total register. However, this method is not able to correct the detected errors, but only a faulty storage.
A memory that is free of errors, i.e. avoiding the use of faulty memory areas, is of great significance for the storage of voice messages. The use of faulty memory areas, which together could exceed a predetermined error rate, would lead to impairments during reproduction, which could result in undesirable audible interference, or even failures.